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Lithium battery over-discharge protection UVP


Lithium battery over-discharge protection UVP
The following is a schematic block diagram and discharge circuit of a battery protection board. The discharge circuit is the part of the green arrow. COUT and DOUT are the charge and discharge control pins respectively, and V- is the important sense pin. To detect various over-discharge and over-charge states of the battery.
When the discharge is overcurrent, it is equivalent to the load decreases, the battery output current increases, and Vbat decreases; as the current increases, the voltage of V-pin sense also increases. When the voltage monitored by V- exceeds a certain value, it is judged as Discharge overcurrent, the protection IC turns off the output pin of DOUT at this time, so that the DSG MOS is turned off and the discharge loop stops.
In the above figure, when the discharge is cut off, V- is sensed with a fixed small current. See the blue curve in the above figure. At this time, the voltage of V- is Vbat. When the load is removed or the load impedance becomes larger, the V- voltage is from Vbat. Decrease gradually, until V- is lower than a certain voltage value, the protection mos opens DOUT again, restores the battery normal discharge path.

At the same time, it should be noted that if charging is performed in the discharge overcurrent protection state, the protection IC will also exit the OCD state, because the charging circuit and the discharging circuit are opposite, as shown in the figure below, the V- voltage is higher than VSS during discharging. On the contrary, when charging, the V-voltage decreases, which satisfies the condition of exiting the discharge overcurrent.

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